"I think all of us are pretty disappointed with the abdication of responsibility by many unionist political leaders," he said.

"No political party, and certainly no responsible political leadership, deserves to serve in a government unless it cooperates and supports fully and unconditionally the police, and calls on its supporters to do so.

"It's true for unionism, it's true for all political parties, and I think that this was not the finest moment for politics in Northern Ireland over the weekend."

The US Envoy said problems needed to be tackled by sustained hard work in communities.

"What you really need is leadership, and unfortunately in the last few days, we haven't seen very much of it," he said.

However, he singled out Ulster Unionist Belfast councillor Fred Cobain for praise for the work he had done over the weekend and in the past weeks.

"When people do stand up and take a courageous stand and exert leadership, they deserve to be recognised," he said.

'No justification'

Irish prime minister Bertie Ahern said that whatever grievances people may have, there was "absolutely no justification for violence". He has asked for a full report from the Joint Secretariat in Belfast.

Sinn Fein president Gerry Adams accused Mr Paisley and Ulster Unionist leader Sir Reg Empey of giving "wrong and negative leadership". He said they could not wash their hands of what happened.

Mr Adams said if he had said "even a measure" of some of the comments made prior to the march, there would have been calls for his arrest.